mold on seedlings

i am starting seedlings in rockwool cubes.i have them covered with plastic with the end open to allow some airflow well it appears i have mold(white fuzz)on the seedlings.are my nubes done for?

or might it be root hairs im looking at?thats kind of what it looks like i have just never seen that much of it.

also since this is my first time using rockwool...seedlings are well above the surface,about what point should i drop the cubes in da dirt.